The present invention relates generally to polishing tools.
More particularly it relates to tools for finish polishing of bevel and flat edges of technical glass on multi-spindle grinding-polishing machines, such as for example xe2x80x9cBovonexe2x80x9d xe2x80x9cZennetixe2x80x9d, Bavellonixe2x80x9d, etc.
In polishing operations on the above mentioned machines, well known felts wheels with a dimensions xe2x80x9cD150 mmxc3x97D70 MMxc3x9725 MM are utilized with cerium dioxide slurry. The polishing wheels rotate with a linear speed about 10 M/sec and a longitudinal speed of glass about 1.0-3.0 m/min, depending on the glass thickness. The polishing wheel and the glass surface contact each other with a pressure of 4-6 bars. Cerium dioxide powder ratio in water varies from 50-100 grams per liter, and circulates through 250-500 liter tanks.
The polishing method which includes the use of the above mentioned felt wheels with a cerium dioxide slurry has substantial disadvantages. Great amounts of powders cause environmental disposal problems. The slurries have pH value about 7 and has to be checked twice a day, because this value increases to 8-8.2 pH and as a result reduces the cerium efficiency. It is necessary to add sulphuric acid to the tank to mixture to provide the right pH value. The user cerium dioxide slurry causes incrustation of the base of a back conveyor which creates irregular surface for glass passage, and correspondingly waved flats, and glass breaking and irregularity of the polishing process. Difficulties in mixing of powders with water cause a non uniformity of the slurry, which can compromise the polishing process, create technical problems, and raise adjustment costs. Also, the incrustations are highly damaging for the machine and seriously compromise the production. The use of slurry and sulphur acid cause deterioration of the machines which reduces a lifetime of the machines and requires expensive repairs. Polishing felt wheels have short service life and can polish about 10,000-15,000 linear inches, depending on the glass thickness.
U.S. Pat. No. 6,033,449 discloses a polishing tool for the above-mentioned processes, which includes cerium dioxide as abrasive, in a corresponding binder. The use of the polishing tool eliminates the above mentioned disadvantages of the polishing process with felt wheels and cerium dioxide slurry. In a polishing process of glass on multi-spindle machine with the tool in accordance with this patent and with technological parameters specified herein above, the use of the wheel with 60-90 shore hardness in a contact zone of the glass with the wheel can cause rapid raise of temperature to about 180-200xc2x0 C. and occurrence of local damaged spaces on the polishing layer of the tool, which creates xe2x80x9cwhitingxe2x80x9d at polishing surfaces of glass. This reduces the quality of polishing. Also, the working layer of the tool must be dressed to take off glazed parts of the polishing tool. It is believed to be clear that it is advisable to eliminate the above mentioned disadvantages.
Accordingly, it is an object of the present invention to provide a polishing wheel, which avoids the disadvantages of the prior art.
In keeping with these objects and with others which will become apparent hereinafter, one feature of present invention resides, briefly stated, in a polishing tool which has a working layer with abrasive particles composed of cerium dioxide and a synthetic resin binder, a body layer, and an intermediate layer located between the working layer and the body layer, wherein the body layer is harder than the working layer, and the intermediate layer is softer than the working layer.
It is advantageous when the ratio hardness between the working layer and the intermediate layer is 4:1.
When the polishing wheel is designed in accordance with the present invention, it eliminates the disadvantages of the prior art. In particular, local vibrations of the polishing wheel are absorbed, a full contact is achieved between the working layer of the polishing tool and a surface of glass to be polished during the polishing process. The polishing wheel has a high wear resistance and a long service life, and provides an efficient polishing, such that each millimeter of thickness of the working layer can polish about 40,000 linear inches of glass.
The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.